The Plant World’s Clean-up Crew – Hyperaccumulators
Hyperaccumulators are plants that are highly effective at accumulating nasty stuff like heavy metals in their “bodies.” So much so, that they can be planted expressly to improve contaminated soil.
Here’s the Wikipedia list of these plants.
You’ll notice some familiar plants on the list: sunflower, alfalfa, barley, kale, broccoli, cabbage, etc. The rapeseed plant, for example, seems very willing to accumulate several different heavy metals where some plants only have one heavy metal friend.
Raised beds of new soil are the usual solution for the home gardener who’s done a soil test and knows that they have contaminated soil but phytoremediation is being used by the US government as a cheap, effective, low-on-labor way to clean up the heavily contaminated Superfund sites.
Grist has an interesting article on what happens or should happen to plants that have been used to clean up toxins.
The Real Know How 